The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Current and future wireless communication systems focus on higher capacity. Two main methods of capacity increase in modern cellular systems are to provide Multiple Input, Multiple Output (“MIMO”) and cell splitting capabilities.
MIMO is a method used to increase the capacity of radio links by using multiple (or multi-port) antennas. Typically, high isolation between antenna ports is required (See, “MIMO Processing for 4G and Beyond: Fundamentals and Evolution” by Mario Marques da Silva, Francisco A. Monteiro, CRC Press, 2014). In the MIMO antenna disclosed in U.S. Pat. No. 8,482,478 entitled “MIMO Antenna System”, absorber material is used for isolation between antenna ports. However, the absorber in that application can cause signal degradation and passive inter-modulation (PIM) issues, which is not acceptable for 3G, 4G/LTE cellular systems.
Existing MIMO antennas (see, for example CommScope R4VP306R for 4×4 MIMO http://www.commscope.com/catalog/wireless/product_details.aspx?id=23598) are bulky and are not multi-beam.
One of the most effective ways to provide cell splitting capabilities is by use of multi-beam antennas (based on Butler Matrix https://www.microwaves101.com/encyclopedias/butler-matrix, U.S. publication 2016/0013,563 entitled “Wideband Twin Beam Antenna Array” and U.S. publication 2011/0205119 entitled “Dual-Beam Sector Antenna and Array”, and U.S. Pat. No. 6,081,233, entitled “Butler Beam Port Combining For Hexagonal Cell Coverage”). U.S. Pat. No. 7,605,768 entitled “Multi-beam Antenna” discloses multi-beam antenna based on spherical lens, but all listed previous examples are not applicable for MIMO because of poor isolation between antenna ports. Antenna ports in other attempted solutions typically exhibit 13-15 dB isolation, which is not enough for a wide operational frequency band.
Therefore, multi-beam antennas attempted by others cannot provide wideband MIMO performance required for current and future cellular communications, and MIMO antennas attempted by others are not suitable for multi-beam operation.
All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Thus, there is still a need for improved antennas can increase capacity in wireless communication systems.